Mechanical refrigeration systems, and related heat transfer devices, such as heat pumps and air conditioners, using refrigerant liquids are well known in the art for industrial, commercial and domestic uses. Chlorofluorocarbons (CFCs) were developed in the 1930s as refrigerants for such systems. However, since the 1980s the effect of CFCs on the stratospheric ozone layer has become the focus of much attention. In 1987, a number of governments signed the Montreal Protocol to protect the global environment, setting forth a timetable for phasing out the CFC products. CFCs were replaced with more environmentally acceptable materials that contain hydrogen, namely the hydrochlorofluorocarbons (HCFCs).
One of the most commonly used hydrochlorofluorocarbon refrigerants was chlorodifluoromethane (HCFC-22). However, subsequent amendments to the Montreal protocol accelerated the phase out of the CFCs and also scheduled the phase-out of HCFCs, including HCFC-22.
In response to the requirement for a non-flammable, non-toxic alternative to the CFCs and HCFCs, industry has developed a number of hydrofluorocarbons (HFCs) which have zero ozone depletion potential. R-410A (a 50:50 w/w blend of difluoromethane (HFC-32) and pentafluoroethane (HFC-125)) was adopted as the industry replacement for HCFC-22 in air conditioning and chiller applications as it does not contribute to ozone depletion. However, R-410A is not a drop-in replacement for R22. Thus, the replacement of R-22 with R-410A required the redesign of major components within heat exchange systems, including the replacement and redesign of the compressor to accommodate the higher operating pressure and volumetric capacity of R-410A, when compared with R-22.
While R-410A has a more acceptable Ozone Depleting Potential (ODP) than R-22, the continued use of R-410A is problematic, due to it's high Global Warming Potential of 2088. There is therefore a need in the art for the replacement of R-410A with a more environmentally acceptable alternative.
It is understood in the art that it is highly desirable for a replacement heat transfer fluid to possess a difficult-to-achieve mosaic of properties, including excellent heat transfer properties, and in particular heat transfer properties that are well matched to the needs of the particular application, chemical stability, low or no toxicity, non-flammability and/or lubricant compatibility amongst others. In addition, any replacement for R-410A would ideally be a good match for the operating conditions of R-410A in order to avoid modification or redesign of the system. The development of a heat transfer fluid meeting all of these requirements, many of which are unpredictable, is a significant challenge.
With regard to efficiency and use, it is important to note that a loss of refrigerant thermodynamic performance or energy efficiency may result in an increase in fossil fuel usage as a result of the increased demand for electrical energy. The use of such a refrigerant will therefore have a negative secondary environmental impact.
Flammability is considered to be an important, and in some cases, an essential property for many heat transfer applications Thus, it is frequently beneficial to use compounds in such compositions, which are non-flammable. As used herein, the term “non-flammable” refers to compounds or compositions which are determined to be non-flammable in accordance with ASTM standard E-681-2001 at conditions described in ASTM standard E-681-2001 at conditions described in ASHRAE Standard 34-2013 and described in Appendix B1 to ASHRAE Standard 34-2013.
US Patent Application 2011/0162410 describes a heat transfer composition based on three components: 1,3,3,3-tetrafluoropropene (R-1234ze), carbon dioxide and a third component selected from difluoromethane (R-32), 1,1-difluoroethane (R-152a), fluoroethane (R-161), 1,1,1,2-tetrafluoroethane (R-134a), propylene (R-1270), propane (R-290) and mixtures thereof. This application discloses that the R-1234ze must be present in the compositions in an amount of at least about 45% by weight, that the CO2 is preferably present in an amount of from about 2% by weight to about 7% by weight, and that the third component is present in an amount of less than 50% by weight. This application discloses that the refrigerant R-125 may also be included in amounts of less than about 40% by weight. This application also discloses the possible use of a fire retarding agent selected from the group consisting of tri-(2-chloroethyl)-phosphate, (chloropropyl)phosphate, tri-(2,3-dibromopropyl)-phosphate, tri-(1,3-dichloropropyl)-phosphate, diammonium phosphate, various halogenated aromatic compounds, antimony oxide, aluminium trihydrate, polyvinyl chloride, a fluorinated iodocarbon, a fluorinated bromocarbon, trifluoro iodomethane, perfluoroalkyl amines, bromo-fluoroalkyl amines and mixtures thereof. Although this application also indicates that the disclosed compositions are useful as low GWP replacements for a number of existing refrigerants, such as R-134a, R-152a, R-1234yf, R-22, R-410A, R-407A, R-407B, R-407C, R507 and R-404a, it does not identify any particular refrigerant for use as a replacement for R-410A.
Applicants have come to appreciate that the compositions disclosed in US Patent Application 2011/0162410 have several disadvantages in connection with potential use as a a refrigerant in systems of the type in which R-410 A has heretofor been commonly used.